Ok, we'll I avoided making a thread for the longest time and after constant searching and failure I feel I need the direct assistance of my TPI brothers...

My problem is that my car runs great, gets good gas mileage but I have trouble at stop lights. When at a stop light the car will idle fine for about a minute or two. After a minute or two, the car will suddenly start to idle funny, like it wants to die, so I pop it in neutral and the idle surges to about 700-1000rpm and prevents it from dying. When the light turns green I start going and it just surges and feels like its missing and hesitating until I really stomp on the gas and all of a sudden after it gets to about 1200rpm it starts driving fine, so I let off the gas and continue as normal. Its been doing this for about a few months. No codes are ever thrown and the car has actually died maybe once or twice at idle but fires right up. There is nothing specific that I can recall that can cause this. Something that I have noticed that might help is that I have a narrowband air/fuel ratio gauge (which is no where near accurate) and when at a stop light, the needle will bounce around like normal at normal idle, but as soon as the idle starts looping/hesitating the needle goes all the way to 0 (full lean?) and does not move. When the gauge gets no signal, it goes to all the way 100% stoich so I don't think its a lack of signal. I thought maybe the gauge was interfering with the oxygen sensor so I disconnected the gauge and it did NOT affect anything. I have replaced the IAC valve with a new unit along with the TPS. I replaced the MAF earlier this year and the oxygen sensor. All new. I also have a fuel pressure gauge and the fuel pressure seems constant and normal. No change in the fuel pressure when it idles funny. The fuel pump was replaced earlier this year aswell and performs awesome on the highway. The spark plugs were recently changed. The nitrous hasn't been used for a few months and the oxygen sensor and spark plugs have not seen NOS usage... I have a MSD cap and rotor along with a MSD blaster coil which, also, were replaced earlier this year... I'm not sure what the hell is causing this. I was hoping it was the TPS which I just replaced this week, but no. I'm not sure what in the world it could be. I'm hoping its not the ecm going bad or bad injectors (but wouldn't the injectors show a change of fuel pressure?)...the fuel filter was also replaced with the new fuel pump... Any idea what it could be? Thanks
-hcr13

 

It sounds like the exhaust is simply building up when at idel like some older carb cars do. When you're sitting at idle, what is your RPM at? Instead of putting your car in nuetral when it starts to act up, try reving it a little with one foot on the brake to keep you from moving. If the exhaust "clears its throat" and it idles good again, I would maybe look into a Catalyic Converter that may be going out. Just an idea.

 

thanks for the reply. I'm sure if I do that, it will clear up, actually, if I just let my foot off the brake and allow the rpms to rise it gets a bit better. I currently have no cat. I've been running catless since last year with no problems... But I'll look into that. Thanks..

 

Did you have this problem before you changed the plugs? IF and thats a big IF, your fuel pressure is good(and you said it SEEMS fine which doesn't sound like your 100% sure!) then I would look at a bad plug wire (age?) bad plug (cracked porcilin when installed??) or weak coil. You didn't say anything about the age or condition of the plug wires and just because something is new, you can't assume its right. I learned THAT lesson along time ago! I would verify 100% that your fuel pressure is correct and then look at an ignition/spark problem. I would guess a bad plug.

 

When I started to have them similar problems, they progressively got worse. Ended up being the injectors going bad. Never threw up any codes. If it starts to get harder to start, usually in the morning for me, I'd look into the injectors
http://fuelinjectorconnection.com/sh...&productId=134
This is the best place to get them for a good price. And excellent customer service too...
I chased problems for months trying not to believe the injectors could cause this. Do an ohm test on them to see if they're all @ .16 ohms

 

The plugs themselves where changed about 2 or 3 months ago for some NGK's so I'm pretty sure its not the plugs. The plug wires where changed sometime last year, so there is a slight chance it could be the wire. I've had plug issues before and it seems those gremlins pop during the higher rpms, not lower...usually. I have an AFPR but its set at stock. I only adjust it when at the track and running nitrous...or until I get a dyno tune. And the fuel pressure is behaving just like it always has. Goes up with rpms/vacuum to stock limits. I'm thinking it is something electrical and fearing its the injectors since those are the main things not replaced... The last time it was behaving like this is when my stock cap and rotor died... The main thing that concerns me is the fact that the oxygen sensor "dies" when this happens... could it possibly be ignition module? Its been replaced a few times before but with other "stock" ones from junkyard cars...

 

BUT....you didn't answer my question. Was the problem there before you changed the plugs. A low rpm missfire that clears up after "X" rpm usually indicated an ignition misfire. I myself have cracked the porceline on a plug and had your exact problem. Also a bad or cheap set of wires can cause the same issue. Lord knows these are not easy plugs to change. My experience with GM ign. modules is that they are good, or they are bad. There no in between. Once they go, they are dead for good.....no fire at all. Maybe others have experienced differently, but not in my 20 years of automotive service. Let the car idle until it starts to miss, then start pulling plug wires one at a time. If you pull a good wire the miss should get worse. If you pull a wire and nothing changes? Suspect a bad plug or wire on that cylinder. Take an ohm reading on the injectors to be safe. Also getting a motovac done to the injection system would be a good thing, regardless of how the ohm readings look. I run ONLY AC Delco plugs in my cars.

 

For under $200, you can have the peace of mind knowing the injectors are good. Do the OHM test, and check them. I was like you, chasing everything but the injectors. I changed: The distributor, cap, rotor, ignition module, plugs, wires, TPS, MAF, fuel pump, fuel filter, fuel pressure reg, fuel pump relay switch, even tried a different set of used stock injectors. Finally fixed with a complete set of new injectors
http://forums.corvetteforum.com/show....php?t=2055067
check out this and make a decision. Thats when I made my decision, and it solved my problem. just my .02

 

Ok thanks for the replies. I have a day off tomorrow and plan on changing a header gasket so I'll also inspect the plug wires and spark plugs. Honestly, I do not recall if the problem was there before or after I changed the plugs its been doing it for a while now and its finally getting on my nerves. I changed the spark plugs because I was running cheap-o Champion plugs and just wanted something with a better reputation. I might buy some more Champion plugs just to see since they are pretty cheap....